Becuase there might be som long delivery times, so if the customer can see a product in stock, and a product out of stock, they might want to buy the in stock instead.And i need the notify me button replaced beacuse if they order a product there isnt in stock i have to order it home, and if they just subsribe the product, i dont have an insurance, that they actually want to buy the product when its there.

Right, so instead of hacking the hell out of VM, why not disable the VM "Check stock", and just modify your VM Template to show the # in stock. Just make that number very big, and next to the "add-to-cart" button so they can't miss it!

Much simpler and cleaner. They can still order, but they will know what is in stock and what is not. You can make template so:

0in stock.You may order out of stock items, or order more than what's in stock,but delivery will be longer in such cases.

How do i make joomla check stock?, or do i manually have to change the stock number on every product? if thats so, that will be way to confusing, then i also have to change every time someone buys a product..

Checking stock does not disable the CHANGE IN STOCK! Check stock only check to see if stock is available. So if you UNTICK check stock, but still put a stock in your products, stock will still decrement as users buy. Try it yourself with a fake order.